Laminating adhesives and/or laminating vehicles or laminating ink vehicles, depending upon the specific nomenclature of the industry, are used in the preparation and/or printing via laminating inks containing the laminating ink vehicles of multi-layer flexible packaging formed from thin polymeric films. A major application market for such flexible packaging is in the packaging of snack foods such as potato chips, pretzels, etc. A construction of a flexible package, for example, consists of an oriented polypropylene (OPP) film which has been laminated with a laminating adhesive with at least one other polymeric film. A different construction for preparing a potato chip package involves extruding molten polyethylene from a die into a nip between a printed film and a second film, such as OPP. Ink coverage can be as high as 100% or greater with multiple layers. An alternative construction consists of a metallized polyethylene terephthalate (PET) base film, an extruded polyethylene (PE), and a reverse printed OPP.
Environmental regulations are driving the industry to water based systems. Water-borne flexo inks are now the major inks used for printing of paper and linerboard. Water-borne inks for printing flexible films, such as oriented polypropylene (OPP), polyethylene, polyethylene terephthalate, and polyvinyl chloride (PVC) have been developed but they have failed to meet the requirements of a good laminating vehicle which include good printability and good bonding to the printed film and yet function as to bond to the laminating extrudate.
Representative literature regarding laminating inks and laminating adhesives as follows:
U.S. Pat. No. 3,033,707 discloses film and foil packaging articles formed by laminating polymeric films, particularly saran-coated regenerated cellulose as well as polyolefins to provide flexible, vapor-proof materials. The adhesive used in bonding the films are based upon polyalkylene imines dispersed within an organic solvent.
U.S. Pat. No. 3,404,114 discloses latexes having adhesion and freeze stability which are suited for use as adhesives for the coatings industry. The latexes comprise from about 1 to 25% of an unsaturated carboxylic acid, from about 50 to 98% of vinylidene monomers or alkyl acrylates and from about 1 to 25% of alkyl amino-alkyl esters of acrylic and methacrylic acid. One of the latex recipes discloses emulsion polymers comprising about 65% ethylacrylate, 31% methyl methacrylate, 1.5% of acrylic and methacrylic acid, and 3% tertiary butylaminoethyl acrylate.
U.S. Pat. No. 3,625,795 discloses a process for depositing an adhesive and for bonding laminates resistant to delamination by spraying an aqueous polymeric latex containing carboxyl functionality onto the material, and the latex droplets deposited as discrete raised spots rather than a continuous film. A wide variety of monomers can be used in preparing the latex which includes lower alkyl esters of acrylic and methacrylic acid, a variety of comonomers, which include conjugated dienes, vinyl halides, vinyl esters, such as vinyl acetate, N-alkylol amides, e.g., N-methylol acrylamide, and other amides. An example shows a latex formed from ethyl acrylate, 2-ethylhexyl acrylate, N-methylol acrylamide, acrylamide, methacrylic acid, and methylene bisacrylamide. The emulsion when applied as discrete droplets impart improved peel strengths to laminates.
U.S. Pat. No. 4,132,831 discloses laminates prepared by a process comprising the addition of a binding amount of a linear, acylated polyalkylenepolyamine. An example shows the application of an aqueous solution of a poly(N-propionyl)ethylenimine to a bleached Kraft paper. Polyethylene film then is applied to the poly(N-propionyl)ethylenimine coated paper and passed through a cold roller. Excellent adhesion had been obtained with this particular acylated polyethyleneimine adhesive.
U.S. Pat. No. 4,483,712 discloses water-borne laminating inks which are printed onto plastic films and subsequently laminated to another plastic film. The ink comprises a binder comprising shellac or copol, water, a lower alcohol, a base, a water-reducible titanium ester chelate and a colorant. The ink is especially suitable for printing on polyolefin films, particularly oriented polypropylene film which has been corona treated.
U.S. Pat. No. 5,037,700 discloses curable, water-borne laminating adhesive. The adhesives suited for producing woven and nonwoven fabrics, oriented and non-oriented polyethylene and polypropylene films, metallic foils and metallized films for use in flexible packaging, graphic arts, etc. A component of the adhesive comprises at least 60% by weight of an alkyl acrylate or methacrylate, 1 to 10% by weight of unsaturated carboxylic acid, and 0 to 39% of a hydroxyalkyl acrylate or methacrylate in methylol acrylamide and a nitrogen-containing monomer such as acrylonitrile, allyl carbamate or an alkylated allyl carbamate.